1. Technical Field
The present invention relates to mobile communications and, more particularly, to signaling between radio network subsystems relating to handover decisions.
2. Discussion of Related Art
Packet Switched (PS) Handover was defined in Release 6 of the relevant 3GPP documents (23.060, 43.129, 24.008, 44.064, 48.018, 25.331, 25.413) based on a GERAN study. To support inter-Radio Access Technology (inter-RAT) PS Handover between UMTS and GSM, signalling had been added in RRC (Uu interface) and RANAP (Iu interface.) at RAN2 #48 (R2-052315) and RAN3 #48. (R3-050924) (28 Aug. 2005-3 Sep. 2005). But in case of inter-RAT PS Handover from UTRAN to GERAN, the SRNC doesn't know whether the target BSS supports PS Handover or not and the SRNC just has to try. Thus, when the SRNC decides to perform PS Handover toward a GERAN cell, if the SRNC doesn't actually know whether the target BSS supports PS Handover or not, SRNC just has to initiate inter-RAT PS Handover and see whether it will receive a positive reply or not. If the PS Handover attempt fails, the SRNC and SGSN processing is wasted on account of the unnecessary message transfer and unnecessary relocation preparation. This problem can be solved easily if RNC knows the target GERAN cell capability, i.e., whether it support PS Handover or not. This GERAN neighbor cell capability can be configured by O&M system or by some signalling in CRNC, i.e., if the O&M system provides information on GERAN neighbor cell capability to the Controlling RNC (CRNC). However this O&M solution also has a limitation in case the CRNC is not also the SRNC. Because the GERAN cell is a neighbor cell of a cell controlled by CRNC (=DRNC), the O&M system will configure the GERAN Neighbour cell capability only in the DRNC. However, the SRNC is the one which decides whether PS Handover will start or not. In the current 3GPP Specifications, there is no means provided for the SRNC to know whether the target GERAN cell supports PS Handover or not.